Cl 2 surface chemistry on Cu/Si1 0 0): an ISS, XPS, and TPD study S.I. Gheyas a , B.L. Strable a , D.R. Strongin a, * , A.P. Wright b a Department of Chemistry, College of Science and Technology, Temple University, Philadelphia, PA 19122, USA b Dow Corning Corporation, Midland, MI 48686-0995, USA Received 4 August 2000; accepted for publication 20 November 2000 Abstract The chemistry of Cl 2 on a Cu/Si1 0 0) at relatively high near surface concentrations of Cu) surface has been in- vestigated using X-ray photoelectron spectroscopy XPS), temperature programmed desorption TPD), and ion scat- tering spectroscopy ISS). XPS and ISS suggested that the deposition of Cu at 120 K on Si1 0 0) resulted in Cu/Si intermixed layers. Heating this surface led to the rapid decrease of Cu in the outermost layer based on ISS, and by 600 K there was no Cu-derived scattering peak even though XPS showed there was a signi®cant amount of Cu in the near surface region. Based on these experimental observations it is postulated that islanding of Cu/Si particles occurred, which is supported by prior studies. Adsorption of Cl 2 on the 120 K-Cu deposited Si1 0 0) surface led to some Cu agglomeration, based on XPS. TPD results showed that SiCl 4 desorbed from this surface at 530 K and SiCl 2 desorbed near 1000 K. The latter peak occurs at the same desorption temperature as SiCl 2 for Cl 2 /Si1 0 0) and is thus attributed to the thermal chemistry of Cl 2 on bare Si1 0 0). It is likely, however, that the 530 K desorption feature was a direct result of the weakened surface bonding of Si in Cu/Si islands, compared to Si on bare Si1 0 0). Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: X-ray photoelectron spectroscopy; Thermal desorption; Copper; Silicides; Chlorine 1. Introduction The Si/Cu bimetallic system is the chemical basis of the direct reaction or Rochow reaction) catalyst used in the modern day silicone industry [1]. It is on this catalytic surface that CH 3 Cl re- actant forms dimethyldichlorosilane, CH 3 ) 2 SiCl 2 , that is the key monomer for the production of silicones. The early application of vacuum-based modern surface science techniques toward inves- tigating the microscopic details of this reaction had limited success due to the low dissociation probability of CH 3 Cl on various Si/Cu surfaces used to model the industrial catalyst [2]. Later studies by Sun et al. showed this problem could be overcome by coadsorbing CH 3 and Cl directly on the Si/Cu catalytic surface in vacuum [3,4]. The product distribution of methylchlorosilanes re- sulting from this preparation procedure turned out to be similar to that obtained at industrial condi- tions with CH 3 Cl as the reactant, thus legitimizing this experimental approach. The development of a Surface Science 474 2001) 129±138 www.elsevier.nl/locate/susc * Corresponding author. Tel.: +1-215-2047119; fax: +1-215- 2041532. E-mail address: dstrongi@nimbus.ocis.temple.edu D.R. Strongin). 0039-6028/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0039-602800)01060-8